The diffusion chamber culture system is being evaluated for the study of hemopoiesis, specifically granulocytopoiesis. Basic studies testing the reliability and reproducibility of the system are carried out. Determinations among the basic studies currently being made are: the pattern of proliferation and maturation of the normal and leukemic human marrow ad blood cells; the pattern of recovery of cells from chambers relative to the number of cells inoculated; the dose of radiation to the chamber-bearing hosts required for optimal cell proliferation; and the suitability of diffusion chamber filter material. After completion of the basic studies, the system will be applied to test the sensitivity of leukemic cells to various drugs. This investigation will hopefully lead to selection of the most suitable drug(s) for treatment of patients. The role of humoral factors in the regulation of granulocytopoiesis is also being evaluated. Peritoneal lavages are performed using potato starch to remove granulocytes from dogs. The cell-free fluid obtained from the lavage is tested for leukocytosis inducing factor (LIF) activity in dogs. This fluid is also tested for in vitro agarplate colony forming cell stimulator activity (CSF). Both LIF and CSF have been noted in the fluids thus far tested. Attempts will be made to separate the CSF and LIF by column chromatography techniques.